3D modelling of the Early Mars Climate and Water cycle

Transcription

1 3D modelling of the Early Mars Climate and Water cycle François Forget 1,Robin Wordsworth 1,, Ehouarn Millour 1, Jean-Baptiste Madeleine 1, Benjamin Charnay 1, Vincent Eymet 2 and Bob Haberle 3 1 Laboratoire de Meteorologie Dynamique, Paris, France 2 Laboratoire Plasma et Conversion de l Energie, Toulouse, France 3 NASA/Ames Research Center, Moffett Field, CA , USA

2 Context: Early Mars More and more clues from minerology and geomorphology suggest that early Mars was different than today, with liquid water flowing. But key questions remains: Were the conditions suitable for liquid water episodic or stable on longer time scales? Role of hydrothermalism (volcanic, impact)? Map of valley networks Map of hydrous minerals: Hynek et al Phyllosilicates and chlorites Hydrated sulfates or zeolites Opaline silica Poulet et al. DPS 2010

3 Early Mars was different: The early Mars Climate enigma Faint Sun CO2 ice clouds? Heating Volcanic Emissions & greenhouse gases? Impact : transient warming? Liquid water Thermal radiation Geothermal flux The question today: what would be the climate on a Mars-like planet with a faint sun (0.75 today) and a thicker CO 2 atmosphere (0.5, 2, 5 bars)?

4 A Global Climate Model (GCM) for early Mars LMDZ grid point dynamical core, 64x48 x15 layers New radiative transfer core: Toon et al. (1989) twostream method for the aerosols Correlated-k for the gaseous absorption Simple parametrisation of CO2 cloud microphysics : condensation, nucleation, transport, sedimentation Surface properties: Fixed surface albedo, thermal inertia Present-day martian topography Circular orbit CO 2 -CO 2 collisioninduced absorption New parametrisation Reduced CO 2 greenhouse effect! (Wordsworth et al. Icarus 2010)

5 0.5 bar Surface CO2 ice

6 1 bar Surface CO2 ice

7 2 bar

8 5 bar

9 CO2 ice clouds warming: 15 to 20K Forget and Pierrehumbert 1997

10 Surface Temperature (bar) Additional greenhouse effect from Water vapor? H2O saturated CO2 atm. 0 C Dry CO2 atm. CO2 surface pressure (bar)

11 Adding a water cycle We include radiative effects of vapour and cloud tracers Assume fixed CCN distribution, but variable mean cloud particle sizes Simple convective relaxation (Manabe scheme), 100% cloud fraction assumed Bucket surface hydrology for the moment Radiative effects (clouds + vapour) Cloud condensation Evaporation Precipitation Surface processes

12 CO2 and H2O cloud cover (2 bars) CO2 ice clouds water clouds

13 3D initial conditions for H2O Polar ice caps

14 3D initial conditions for H2O water ocean

15 2 bar, icecaps

16 2 bar, ocean

17 5 bar, icecaps

18 5 bar, icecaps

19 5 bar, ocean

20 5 bar, ocean

21 Wait a minute :5 bars of CO 2??? The initial Mars inventory was probably > 10 bars BUT recent studies suggest a much thinner inventory for the Noachian Martian atmosphere: Primordial atmosphere of Mars was probably removed quickly (Tian et al., 2009) Tharsis outgassing (Phillips et al.,2001) has probably been overestimated. Morschhauser 2011: In the Noachian, mbar CO 2 can be outgassed After the heavy bombardment, atmospheric escape was probably weak (Leblanc and Johnson 2002; Barabash et al. 2007; Lammer et al. 2011) 500 mbar of CO 2 may be an upper limit on ancient Mars?

22 Ongoing work: Mars with ~500 mbar of CO 2 We Need to explore the behaviour of a cold icy Mars with ~500 mbar of CO2. It will still be very different than today : Cold traps in the mountains (like on Earth) Liquid water much more stable Larger ice inventory? (less ice sequestered?) Some greenhouse effect Possible transient melting of seasonal ice and glaciers? Ice trapped at the poles or available in many places to melt with impacts or volcanic events?

23 Ongoing work: Mars with ~500 mbar of CO 2 Starting with limited polar caps: Surface ice (kg/m2) : initial state Ps = 0.5 bar obliquity=25

24 Ongoing work: Mars with ~500 mbar of CO 2 Starting with limited polar caps: Surface ice (kg/m2) : AFTER 50 years Ps = 0.5 bar obliquity=25

25 Ongoing work: Mars with ~500 mbar of CO 2 Starting with limited polar caps: HIGHER obliquity (45 ) Surface ice (kg/m2) : Initial state Ps = 0.5 bar obliquity=45

26 Starting with limited polar caps: HIGHER obliquity (45 ) Surface ice (kg/m2) : AFTER 50 years Ps = 0.5 bar obliquity=45

27 Starting with limited polar caps: REMOVING THARSIS Next step: remove the LHB basin Surface ice (kg/m2) : initial state Ps = 0.5 bar obliquity=25

28 Starting with limited polar caps: REMOVING THARSIS Next step: remove the LHB basin Surface ice (kg/m2) : AFTER 50 years Ps = 0.5 bar obliquity=25

29 Starting with a global ice sheet on the colder plateau Surface ice (kg/m2) : Initial state Ps = 0.5 bar obliquity=25

30 Starting with a global ice sheet on the colder plateau Surface ice (kg/m2) : AFTER 50 years Ps = 0.5 bar obliquity=25

31 Starting with a global ice sheet on the colder plateau MELTING ice (arb. units) : AFTER 50 years Ps = 0.5 bar obliquity=25

32 Starting with a global ice sheet on the colder plateau MELTING ice (arb. units) : AFTER 50 years Ps = 0.5 bar obliquity=25

33 A ongoing study : determine where the ice reservoir will stabilize

34 A ongoing study : determine where the ice reservoir will stabilize

35 A ongoing study : determine where the ice reservoir will stabilize

36 A ongoing study : determine where the ice reservoir will stabilize

37 A ongoing study : determine where the ice reservoir will stabilize Impacts? T>0ºC for short period : snow and glacier melt Geothermal heating

38 Preliminary conclusions 3D GCM simulations of an early Mars CO 2 - H 2 O climate and water cycle. CO2 gas greenhouse effect lower than previously thought (weaker Collision Induced Absorption) Significant warming by CO 2 clouds Adiabatic warming in lower plains. Warm, dry Mars possible, BUT with very thick CO 2 atmosphere Colder, icy ancient Mars scenario with a few hundreds of mbars currently explored. More work required to better understand where the water reservoir will be stabilized, melting,etc To be continued